Metal sheet coated with thermoplastic resin and can obtained therefrom

ABSTRACT

A thermoplastic-resin-coated metal sheet in which the thermoplastic resin has been applied to the metal sheet without through an adhesive primer and which, even after having been formed into a can, is excellent in impact resistance at low temperatures and resistance to corrosion by acid contents; and a can obtained from the coated metal sheet. The thermoplastic-resin-coated metal sheet is obtained by coating a metal sheet with a thermoplastic resin composition comprising a blend of a polyester resin with a polyolefin resin or polyolefin elastomer. This metal sheet is formed into a can through drawing/ironing with thickness reduction.

TECHNICAL FIELD

The present invention concerns a thermoplastic resin-coated metal sheetand, particularly, a thermoplastic resin-coated metal sheet in which thecoating resin is excellent in impact resistance at low temperature, aswell as a can obtained by forming the same.

BACKGROUND ART

In recent years, cans formed by coating a polyester resin on a metalsheet and improved with thickness reduction ratio for side wall portionsby applying severe forming such as thickness-reducing drawing orthickness-reducing ironing have been used as cans mainly for drinkapplications. In a case of forming a polyester resin coated metal sheetby applying severe such as wall reducing drawing or wall reducingironing, it is necessary to coat in a non-orientation state capable ofattaining excellent fabricability such that the resin is not peeled uponforming or cracks are not formed to the resin.

However, when applying thickness-reducing drawing or thickness-reducingironing is applied to a resin-coated metal sheet with a non-orientationstate of a polyester resin, then applying coating printing to the outersurface of the can and heating for baking, since the upper portion ofthe can is thermally set in a state where it is molecularly oriented inthe direction of a height of the can by the fabrication, elongation ofthe not oriented resin in the circumferential direction of the can isextremely small to become brittle. Particularly, cracks tend to beformed to the resin layer by mere collision between cans to each other,particularly, at low temperature. Further, since the portion for the canbottom scarcely undergoes the forming, the resin crystals are grown intoa coarse state and brittled upon heating for baking after the coatingprinting also tending to cause cracks upon receiving impactsparticularly at low temperature.

That is, a polyester resin-coated metal sheet in a non-orientation stateis poor in the impact resistance, particularly, the impact resistance atlow temperature after formed into the can.

Poor impact resistance after forming can be improved by interposing anadhesive primer between the polyester resin and the metal sheet uponcoating the polyester resin on the metal sheet. However, a method ofinterposing the adhesive primer may possibly cause undesired effects onthe environment due to evaporation of organic solvents and, further,requires surplus steps of coating and drying to increase the cost.Further, in a case where acidic contents at pH of 5 or less are filled,the underlying metal sheet may sometimes be corroded in the upperportion of the can undergoing high degree of fabrication after lapse ofa long time.

The present invention intends to provide a thermoplastic resin-coatedmetal sheet in which a resin layer, after applying severe forming to athermoplastic resin-coated metal sheet where the resin layer aftercoating to the metal sheet is in a non-oriented state, is excellent inimpact resistance, particularly, impact resistance at low temperature,coated to the metal sheet without interposing an adhesive primer and isexcellent in corrosion resistance to acidic contents even in a casewhere it is formed into a can, as well as a can using the same.

DISCLOSURE OF THE INVENTION

According to the present invention, it is provided a thermoplasticresin-coated metal sheet in which a thermoplastic resin compositioncomprising a blend of one or more of polyester resins and at least onepolyolefin ingredient selected from the group consisting of polyolefinresins and polyolefin elastomers is coated on at least one surface of ametal sheet in a substantially non-orientation state.

Further, according to the present invention, a can using a thermoplasticresin-coated metal sheet is provided.

That is, in the present invention, as the polyolefin ingredient in thethermoplastic resin composition forming the coating layer, a polyolefinresin, a polyolefin elastomer, or a combination of a polyolefin resinand a polyolefin elastomer can be used.

Further, a polyolefin resin layer formed substantially in a not-yetoriented state can be disposed above the coating layer of thethermoplastic resin composition or in the lower layer to the coatinglayer (surface of metal sheet).

In the thermoplastic resin composition used in the present invention, itis preferred that the ratio of a melt viscosity upon heat melting thepolyolefin ingredient (polyolefin resin or polyolefin elastomer, or acombination of the polyolefin resin and a polyolefin elastomer) (VPOL)and the melt viscosity upon heat melting the polyester resin (VPES),that is, VPOL/VPES is 1.2 or less.

The polyolefin resin used as the polyolefin ingredient in the presentinvention is preferably a resin comprising one or more of 1-alkenepolymer resins having a number of carbon atoms of 2 to 8, and the1-alkene polymer resin is preferably one of polyethylene, polypropyleneand ethylene-propylene copolymer. Further, as the polyolefin resin, apolyolefin resin polymerized by a metallocene catalyst can also be used.Further, a modified polyolefin resin modified with one of maleic acidhydride, acrylic acid, acrylic acid ester, or diglycidyl methacrylatemay be used also as the polyolefin resin.

Further, as the polyolefin elastomer used for the polyolefin ingredient,an in-plant produced ethylene-propylene copolymerized elastomer with amelt flow rate (MFR, 230° C.) of from 0.4 to 30 (g/10 min) is suitable.

In the present invention, the polyester used for the thermoplastic resincomposition is a polyester resin comprising ester repetitive units of atleast one of ethylene terephthalate, ethylene isophthalate, ethylenenaphthalate, ethylene adipate, butylenes terephthalate, butyleneisophthalate, butylene naphthalate and butylene adipate, with theintrinsic viscosity being preferably from 0.5 to 1.5 and, particularly,ethylene terephthalate/ethylene isophthalate copolymer or polybutyleneterephthalate is preferred.

The polyester resin in the polyester resin layer capable of forming inan upper layer or a lower layer to the coating layer of thethermoplastic resin composition is preferably ethyleneterephthalate/ethylene isophthalate copolymer.

Further, the thermoplastic resin composition preferably contains 1 to30% by weight of the polyolefin ingredient and preferably contains 70 to95% by weight of the polyester resin.

The thermoplastic resin-coated metal sheet according to the presentinvention is produced by heat melting a thermoplastic resin composition,directly extruding the same from a T-die onto a metal sheet for coating,or heat melting a thermoplastic resin composition, extruding the samefrom a T-die to a casting roll, cooling to solidify the same into a filmand then hot press bonding the film on the metal sheet.

In the thermoplastic resin-coated metal sheet according to the presentinvention, it is preferred that the olefin ingredient in the coatinglayer comprised of the thermoplastic resin composition is present beingdispersed with a size of 1 to 10 μm in the extruding direction of theresin and 0.1 to 2 μm in the direction perpendicular to the resinextruding direction.

Further, in the thermoplastic resin-coated metal sheet, the metal sheetis preferably one of electrolytic chromic acid treated steel sheet,tin-plated steel sheet or aluminum alloy sheet.

BEST MODE FOR PRACTICING THE INVENTION

The present invention provides a thermoplastic resin-coated metal sheethaving a coating layer of a thermoplastic resin composition comprising ablend of a polyester resin and a polyolefin ingredient (at least onemember selected from the group consisting of polyolefin resins andpolyolefin elastomers) at least on one surface of a metal sheet and,optionally, a polyester resin layer formed to an upper layer and/orlower layer of the coating layer, as well as a can obtained by formingthe same, and the resin layer is excellent in impact resistance and,particularly, impact resistance at low temperature and also excellent incorrosion resistance to acidic contents even in a case of coating athermoplastic resin coating without interposing an adhesive primer to ametal sheet and applying severe forming such as thicknessreducing-drawing or thickness-reducing ironing.

The present invention is to be described specifically.

In the thermoplastic resin composition comprising the blend of thepolyester resin and the polyolefin ingredient, a polyolefin resin and apolyolefin elastomer are used as the polyolefin ingredient each alone orin combination.

In the polyolefin ingredient and the polyester resin, it is preferredthat the ratio of the melt viscosity in a case of melting the respectiveresin pellets is in a predetermined range. That is, it is preferred thatVPOL/VPES is 1.2 or less where VPOL represents the melt viscosity uponheat melting of the polyolefin ingredient (polyolefin resin, polyolefinelastomer or a combination of both of them) and VPES represents a meltviscosity upon heat melting of polyester resin. The reason will bedescribed below.

The coating layer of the thermoplastic resin composition (heareinaftersometimes simply referred to as a thermoplastic resin film) is formed byheat melting resin pellets and extruding the blended resin from a T-dieof an extruder directly onto a long strip-like metal sheet unwound froman uncoiler, or heat melting a resin heat melted from a polyester resinpellets separately and heat melted and blended resin from respectiveseparate extruders, then coextruding them from a T-die having aplurality of die nozzles directly onto a long and strip-like metal sheetunwound from an uncoiler, and pressing the same by pressing rolls to ametal sheet. Alternatively, it is formed by extruding a heat meltedresin in the same manner as described above from a T-die of an extruderonto a casting roll, cooling to solidify the same to form a film, thenabutting the film against the heated long strip-like metal sheet whichis unwound from an uncoiler and heated, and press bonding by sandwichingthe same between a pair of laminate rolls by using an known laminater.In each of the preparation method, when the molten resin is extendeddownwardly, that is, in the longitudinal direction when the heat-meltedblend resin is extruded from the T-die onto the metal sheet or thecasting roll, since the molten resin is stretched downwardly, that is,in the longitudinal direction gravitationally, anisotropy occursalthough little in the resin film. In a case where VPOL/VPES exceeds1.2, anisotropy of the film of the blend resin increases to lower therigidity of the film in the lateral direction compared with that of thelongitudinal direction, and tend to cause lateral cracking upon exertionof impact after coating to the metal sheet. With a view point describedabove, it is preferred that VPOL/VPES is 1.2 or less.

The polyolefin resin used as the polyolefin ingredient can includeresins comprising one or more of 1-alkene copolymer resins with a numberof carbon atoms of 2 to 8. The 1-alkene copolymer resin with the numberof carbon atoms of 2 to 8 can include, for example, low densitypolyethylene, medium density polyethylene, high density polyethylene,polypropylene, polybutene-1, polypentent-1, polyhexene-1, polyheptene-1,polyoctene-1, ethylene-propylene copolymer, ethylene-1-butene copolymer,and ethylene-hexene copolymer. Among them, in-plant producedethylene-propylene copolymer is preferred. Further, as the polyolefinresins, use of a polyolefin resin by a metallocene catalyst is preferredsince it forms less oligomers that may give effects on the flavor ofcontents.

Further, modified polyolefin resins formed by modifying the polyolefinresin, for example, polyethylene or polypropylene, for example, with oneof maleic acid anhydride, acrylic acid, acrylic acid ester, acrylic acidionomer, and diglycidyl methacrylate may also be used. The modifiedpolyolefin resin blended at a ratio of 1 to 100% by weight to thenot-modified polyolefin resin is used preferably as the polyolefin resinsince the polyolefin ingredient is finely dispersed in the polyesterresin.

As the polyolefin elastomer, use of an ethylene-propylene copolymerelastomer having a melt flow rate (MFR, 230° C.) of 0.4 to 30 (g/10min), particularly, 0.8 to 25 g/10 min is preferred. In a case where MFRis less than the range described above, the melt viscosity isexcessively higher relative to the polyester resin when the resin isheat melted and the grains of the polyolefin resin dispersed in thepolyester resin is grown excessively to deteriorate the impactresistance. On the other hand, in a case where it exceeds the rangedescribed above, the impact resistance of the polyolefin elastomer perse is poor, and the resin blended with the polyester resin is also poorin the impact resistance. Further, it is preferred that theethylene-propylene copolymer elastomer is in-plant produced.

The blending ratio of the polyolefin ingredient to the thermoplasticresin composition (polyolefin ingredient content in the thermoplasticcomposition) is preferably 1 to 30% by weight. In a case where theamount of the polyolefin ingredient is small, the thermoplastic resincomposition after coating on the metal sheet lacks in the impactresistance. In a case where the amount of the polyolefin ingredient isunnecessarily large, the transparency of the thermoplastic resincomposition decreases to make the anisotropy larger and the hardness isalso decreased, so that the resin surface tends to be injured.

As the polyester resin which is blended with the polyester resin to forma thermoplastic resin composition, those comprising ester repetitiveunits of at least one of ethylene terephthalate, ethylene isophthalate,ethylene naphthalate, ethylene adipate, butylenes terephthalate,butylenes isophthalate, butylenes naphthalate and butylenes adipate canbe used alone or as a blend of two or more them. Further, it is alsopossible to use those other than described above that use sebasic acid,trimellitic acid or azelaic acid as the acid ingredient for the esterunit, or those of three or more carbon atoms, for example, propyleneglycol, diethylene glycol, neopentyl glycol, and pentaerythritol as thealcohol ingredient for the ester unit.

In the present invention, ethylene terephthalate/ethylene isophthalatecopolymer or polybutylene terephthalate is used suitably as thepolyester resin. Particularly, a polyester resin comprising 5 to 15 mol% of ethylene isophthalate and 85 to 95 mol % of ethylene terephthalateis excellent in fabricability and cause no cracks in the resin layereven when severe forming such as thickness-reducing drawing is appliedafter blending with the polyolefin ingredient and lamination onto themetal sheet and is also excellent in adhesion with the metal sheet.Further, in a case where it is in contact with contents filled in thecan, it does not deteriorate flavor or taste of the contents and showfavorable flavor property.

Further, polybutylene terephthalate is easily mixed with the polyolefiningredient (particularly, polyolefin resin) and in a case where it isblended, for example, with a polyolefin resin, the polyolefin resin isdispersed more finely in the blend resin, which is effective for theimprovement of the impact resistance and the fabricability. Further,polybutylene terephthalate has high crystallization rate and in a casewhere a coated metal sheet having a coating layer of a thermoplasticresin composition is formed into a can and then the can is heated, forexample, by outer surface coating, it has a feature of suppressing thegrow of brittle and cause crystals. Accordingly, use of polybutyleneterephthalate is extremely effective for the improvement of the impactresistance at low temperature as an object of the present invention. Inaddition, a thermoplastic resin composition blended with polybutyleneterephthalate is excellent in water degradation resistance (hydrolysisresistance), and the can having the coating layer comprising thethermoplastic resin composition shows less lowering of the molecularweight of the resin even when left for long time with aqueous contentsbeing filled therein and, accordingly, can maintain stable favorableimpact resistance for a long time.

In the present invention, since it is on the premise that thethermoplastic resin composition comprising a blend of the polyesterresin and the polyolefin ingredient described above is used in anon-orientation state excellent in the fabricability in order to enablesevere fabrication such as thickness-reducing drawing- orthickness-reducing drawing and ironing without causing cracking,chipping, scraping and peeling of the resin, it is necessary to increasethe intrinsic viscosity of the resin and strengthen the resin.Accordingly, the intrinsic viscosity of the polyester resin preferablyranges from 0.5 to 1.5 and, more preferably, ranges from 0.8 to 1.2. Ina case where polyester resin with an intrinsic viscosity of less than0.5 is used, the strength of the resin is lowered extremely making itdifficult for application use of thickness reduced drawn can orthickness reduced drawn and ironed can. In addition, flavor property ofcontents tends to be deteriorated. On the other hand, in a case wherethe intrinsic viscosity of the resin exceeds 1.5, melt viscosity uponheat melting the resin increases extremely making it extremely difficultfor the operation of coating the thermoplastic resin composition on themetal sheet.

The blend ratio of the polyester resin to the thermoplastic resincomposition (content of the polyester resin in the thermoplastic resin)is preferably from 70 to 95% by weight. In a case where the amount ofthe polyester resin is small, the transparency is reduced and theanisotropy increases in the thermoplastic resin composition and,further, the hardness is decreased as well, so that the resin surfacetends to be injured. Further, if the amount of the polyester resin isunnecessarily large, the transparency is reduced and the anisotropyincreases in the thermoplastic resin composition and, further, thehardness is decreased as well, so that the resin surface tends to beinjured.

Particularly, in a case where the ethylene terephthalate/ethyleneisophthalate copolymer described above is used as the polyester resin,when the blend ratio is less than 70% by weight, the fabricability ofthe thermoplastic resin composition after coating on the metal sheet ispoor, whereas when the blend ratio exceeds 95% by weight, dispersedparticles of the polyolefin ingredient in the resin composition becomecoarser, causing a worry of deteriorating the impact resistance and theworkability. Further, in a case where polybutylene terephthalatedescribed above is used as the polyester resin, when the blend ratio isless than 70% by weight, the dispersed particles of polyolefiningredient in the resin composition become coarser making it difficultto obtain a sufficient impact resistance. When the blend ratio exceeds95% by weight, the resin layer is clouded to deteriorate the appearanceby heating of the can such as outer surface coating after forming theresin coated metal sheet into a can. Accordingly, it is most suitable inthe present invention that the ethylene terephthalate/ethyleneisophthalate copolymer and polybutylene terephthalate is used togethersuch that the total amount is within the range of the blend ratiodescribed above.

In the present invention, a polyester resin layer can be formed for theupper layer and/or lower layer to the coating layer comprising thethermoplastic resin composition described above and a coating of atwo-layered or three-layered structure as a whole can be formed on atleast one surface of the metal sheet.

As the polyester resin for forming the upper layer or the lower layer,the same polyester resin as used in the formation of the thermoplasticresin composition can be used, and ethylene terephthalate/ethyleneisophthalate copolymer is suitable since this is excellent in the flavorproperty to contents and the fabricability and is also excellent in theadhesion to the metal sheet as described previously. In the copolymerdescribed above, a copolymer comprising 3 to 15 mol % of ethyleneisophthalate and 85 to 97 mol % of ethylene terephthalate is preferredfor the upper layer, and a copolymer comprising 10 to 25 mol % ofethylene isophthalate and 75 to 90 mol % of ethylene terephthalate ispreferred for the lower layer.

Further as described above, the resin coating in the thermoplasticresin-coated metal sheet according to the present invention has acoating layer of a thermoplastic resin composition at least comprising apolyester resin and a polyolefin ingredient and includes a case wherethe coating layer comprises a single-layered structure, a case of a2-layered structure in which the polyester resin layer is formed toeither one of the upper layer or the lower layer of the coating layerand a case of a three-layered structure in which the polyester resinlayer is formed to the upper layer and the lower layer of the coatinglayer. In the case of the single-layered structure comprising only thecoating layer of the thermoplastic resin composition, the thickness ispreferably within a range from 5 to 50 μm. In a case of the two-layeredstructure of the coating layer and the polyester resin layer, it ispreferred that the thickness of the upper layer ranges from 3 to 15 μm,the thickness of the lower layer ranges from 2 to 47 μm and, further,the entire thickness ranges from 5 to 50 μm. In a case of thethree-layered structure comprising the coating layer and the polyesterresin layers, it is preferred that the thickness of the polyester resinlayer for the upper layer ranges from 2 to 10 μm, the thickness of thecoating layer as the intermediate layer ranges from 5 to 30 μm and thethickness of the polyester resin layer for the lower layer ranges from 3to 10 μm.

The thermoplastic resin film constituting the resin coating describedabove may be formed by extruding a resin obtained by heat melting andblending resin pellets to be blended at a temperature higher by 20 to40° C. than the melting point of the polyester resin having the highestmelting point among the resins to be used (about 200 to 300° C.) from aT-die of an extruder directly onto a long strip-like metal sheetre-wound from a uncoiler, or heat melting a resin obtained by separatelyheat melting polyester resin pellets at a temperature higher by 20 to40° C. than the melting point and the heat melted and blend resindescribed above by separate extruders respectively, then co-extrudingthem from a T-die having a plurality of die nozzles directly on a longstrip-like metal sheet unwound from an uncoiler, pressing them againstthe metal sheet by press bonding rolls and then quenching directly inwater thereby preparing a thermoplastic resin film-coated metal sheet,or by extruding the heat melted resin in the same manner as describedabove from a T-die of an extruder onto a casting roll, cooling tosolidify the same into a film, then re-winding from an uncoiler andabutting the film to a long strip-like metal sheet heated to atemperature higher by 20 to 40° C. than the melting point of thepolyester resin, press bonding them while sandwiching between a pair oflaminate rolls by means of a known laminator and immediately quenchingthem in water thereby preparing a thermoplastic resin film-coated metalsheet. Further, in a case of application use not applied with severeforming as in the present invention, heat melted resin may be extrudedfrom a T-die of an extruder onto a casting roll, then stretched in auni-axial direction (longitudinal direction) or bi-axial direction(longitudinal direction and lateral direction) and then heat set to forma film in which crystal molecules are oriented, which may be laminatedonto the metal sheet.

In the thermoplastic resin composition in which the polyester resin andthe polyolefin ingredient are heat melted as described above (blendresin), the polyolefin resin or the polyolefin ingredient is finelydispersed in the matrix of the polyester resin. When the heat meltedblend resin in this state is extruded from the T-die onto the metalsheet or the casting roll, the molten resin is gravitationally stretcheddownward although little. In this process, the polyolefin ingredient(polyolefin resin or polyolefin elastomer) dispersed finely in thematrix of the polyester resin is stretched in the direction ofgravitational force and dispersed in the matrix of the polyester resinbeing dispersed in a fibrous state after the blend resin has been cooledto solidify to the metal sheet on the casting roll. In the dispersionstate, when the resin coated metal sheet is applied withthickness-reducing drawing or thickness reducing drawing and ironing toform a can, a dispersed fibrous blend resin is sometimes visible withnaked eyes. The fibrous blend resin is no more visible with naked eyeswhen it is 10 μm or less in the extruding direction and 2 μm or less inthe direction perpendicular to the extruding direction when extrudedfrom the T-die. Accordingly, it is preferred in the present inventionthat the olefin ingredient in the thermoplastic resin composition ispresent being dispersed with a size of 1 to 10 μm in the extrudingdirection of the resin (length in the film direction) and 0.1 to 2 μm inthe direction perpendicular to the extruding direction of the resin(length in the lateral direction of the film) in the coating layer ofthe thermoplastic resin composition after preparing the thermoplasticresin-coated metal sheet.

As the substrate for the thermoplastic resin-coated metal sheet of thepresent invention, various kinds of surface treated steel sheets such aselectrolytic chromic acid treated steel sheet (tin free steel,hereinafter represented by TFS) or tin-plated steel sheet (tin sheethereinafter represented by tin sheet), and aluminum alloy sheet whichare usually used generally as materials for cans can be used. For thesurface treated steel sheets, TFS having, on a steel sheet, a 2-layeredfilm comprising a lower layer composed of metallic chromium in amembrane amount of 10 to 200 mg/m² and an upper layer composed ofchromium hydrate oxides in a membrane amount of 1 to 30 mg/m² based onthe chromium content is preferred, which has a sufficient adhesiveproperty with the thermoplastic resin film according to the presentinvention and also has corrosion resistance. Preferred film sheets arethose obtained by applying plating in a plating amount of 0.1 to 11.2g/m² on the surface of the steel sheet and, forming thereon, a 2-layeredfilm comprising metallic chromium and chromium-hydrate oxides in anamount of membrane from 1 to 30 mg/m² based on chromium content, orforming a single layered film comprising only chromium hydrate oxides.In any of the cases, the steel sheets as the substrates is preferably acold rolled low carbon steel sheet used generally as the material forcans. The thickness of the steel sheet is preferably from 0.1 to 0.32mm. For the aluminum alloy sheet, JIS 3000 series or 5000 series ispreferred, and preferred are those applied with an electrolytic chromicacid treatment to the surface to form a 2-layered film comprising alower layer composed of metallic chromium in a film amount of 0 to 200mg/m² and an upper layer comprising chromium hydrate oxides in amembrane amount of 1 to 30 mg/m² based on the chromium content, or thoseapplied with a chromium phosphate treatment to deposit 1 to 30 mg/m² ofa chromic ingredient based on the chromium content and 0 to 30 mg/m² ofphosphoric ingredient based on the phosphorus content. The thickness ofthe aluminum alloy sheet is preferably from 0.15 to 0.4 mm.

EXAMPLE

The present invention is to be described more specifically by way ofexamples.

Example 1

(Specimen Nos. 1-6, 11-17, 26-32)

A long strip-like electrolytic chromic acid treated steel plate(hereinafter referred to as TFS) was re-wound at a rate of 150 m/minfrom an uncoiler, and pellets comprising a polyester resin shown inTable 1 (represented by PES in the table here and hereinafter), apolyolefin resin (represented by POL in the table here and hereinafter)and/or a polyolefin elastomer (represented by PEL in the table here andhereinafter), or only comprising the polyester resin were heat melted ata temperature higher by about 30° C. than the melting point of thepolyester resin while varying the kneading time by using an extruder toform a blend resin, then fed to a T-die and extruded from a die nozzleon one surface of TFS, that is, one surface to be an inner surface of acan (represented by inner surface in the table herein and hereinafter).Simultaneously, pellets of a polyester resin incorporated with 20% byweight of white titanium oxide shown in Table 1 were heat melted at atemperature higher by about 30° C. than the melting temperature of thepolyester resin using an extruder, then fed into a T-die and extrudedfrom the die nozzle on the other surface of TFS, that is, one surface tobe an outer surface of the can (represented by outer surface in thetable here and hereinafter). Then, after sandwiching the TFS to whichthe resin layer was extruded on both surface thereof by using a pair ofpress bonding rolls, they were directly quenched in water to preparethermoplastic resin-coated metal sheets of Specimen Nos. 1-6, 11-17,26-0.32 in Tables 2 and 3.

(Specimen Nos. 18, 19)

A long strip-like tin sheet was re-wound from an uncoiler at a rate of150 m/min and heated, and pellets of the polyester resin and thepolyolefin resin shown in Table 1 were heat melted at a temperaturehigher by about 30° C. than the melting point of the polyester resinwhile varying the kneading time by using an extruder to form a blendresin, the polyester resin shown in Table 1 was heat melted at atemperature higher by about 30° C. than the melting point of thepolyester resin by using a separate extruder, then they were fed to aT-die having two die nozzles and co-extruded on one surface of a tinsheet from the die nozzles such that the blend resin layer containingthe polyolefin resin was in contact with the tin sheet. Simultaneously,pellets of the polyester resin incorporated with 20% by weight of whitetitanium dioxide shown in Table 1 was heat melted at a temperaturehigher by about 30° C. than the melting point of the polyester resin byusing an extruder, fed to a T-die and then extruded from the die nozzleto the other surface of the heated tin sheet to be an outer surface of acan. Then, sandwiching the tin sheet to which the resin layer wasextruded on both surface thereof by using a pair of press bonding rollsand, they were directly quenched in water to prepare thermoplasticresin-coated metal sheets of Specimen Nos. 18 and 19 in Table 3.

(Specimen Nos. 7-10, 20-23)

Pellets of the polyester resin and the polyolefin resin or polyolefinelastomer shown in Table 1 were heat melted at a temperature higher byabout 30° C. than the melting point of the polyester resin while varyingthe kneading time by using an extruder to form a blend resin, then fedinto a T-die, extruded from a die nozzle, followed by trimming andtaken-up to a coiler as a non-orientation film. Further, pellets of thepolyester resin incorporated with 20% by weight of white titaniumdioxide shown in Table 1 were heat melted at a temperature higher byabout 30° C. than the melting point of the polyester resin by using anextruder, fed into a T-die, extruded from a die nozzle, followed bytrimming and then taken up as a non-orientation film to a coiler. Then,a long strip-like aluminum alloy sheet was rewound at rate of 150 m/minfrom an uncoiler and heated, a blend resin film was abutted while beingre-wound from the coiler to one surface to be an inner surface of a canand, at the same time, a white polyester film was abutted while beingre-wound from the coiler to the other surface to be an outer surface ofthe can. Then, after sandwiching the aluminum alloy sheet to which theresin layer was extruded on both surface thereof by using a pair ofpress bonding rolls, they were directly quenched in water to preparethermoplastic resin-coated metal sheets of Specimen Nos. 7-10 and 20-23in Tables 2 and 3.

(Specimen Nos. 24, 25)

Pellets of the polyester resin and the polyolefin resin shown in Table 1were heat melted at a temperature higher by about 30° C. than themelting point of the polyester resin while varying the kneading time byusing an extruder to form a blend resin, the polyester resin shown inTable 1 was heat melted at a temperature higher by about 30° C. than themelting point of the polyester resin by using a separate extruder, thenfed into a T-dye having two die nozzles, co-extruded from the dienozzles, followed by trimming and then taken up as two layers of anon-orientation film to a coiler. Further, pellets of the polyesterresin incorporated with 20% by weight of white titanium dioxide shown inTable 2 and 3 were heat melted at a temperature higher by about 30° C.than the melting temperature of the polyester resin by using anextruder, fed into a T-die, extruded from the die nozzle, followed bytrimming and then taken-up as a non-orientation film to a coiler. Then,a long strip-like tin sheet was re-wound at a rate of 150 m/min from anuncoiler, and heated, and the two-layered resin film was abutted againstone surface thereof to be an inner surface of a can while being re-woundfrom the coiler such that the blend resin layer containing thepolyolefin resin was in contact with the tin sheet. At the same time,the white polyester film was abutted, while being re-wound from thecoiler to the outer surface of the can. Then, after sandwiching the tinsheet to which the resin layer was extruded on both surface thereof byusing a pair of press bonding rolls, they were directly quenched inwater to prepare thermoplastic resin-coated metal sheets of SpecimenNos. 24 and 25 in Table 3.

The metal sheets applied with the surface treatment shown below wereused as the three types of the metal sheets described above.

-   (1) Electrolytic chromic acid treated steel sheet (indicated as TFS    in the table)    -   Sheet thickness: 0.18 mm    -   Amount of metallic chromium: 160 mg/m²    -   Amount of chromium hydrate oxide: (as chromium) 19 mg/m²    -   Heating temperature: temperature higher by about 30° C. than the        melting point of the polyester resin-   (2) Tin sheet (indicated as ET in the table)    -   Sheet thickness: 0.18 mm    -   Amount of tin plating: 0.2 g/m²    -   Amount of chromium hydrate oxide: (as chromium) 9 mg/m²    -   Heating temperature: 200° C.-   (3) Aluminum alloy sheet (JIS 5052H 39) (indicated as Al in the    table)    -   Sheet thickness: 0.26 mm    -   Amount of membrane: (as phosphorus) 11 mg/m² (as chromium) 7        mg/m²    -   Heating temperature: temperature higher by about 30° C. than the        melting point of the polyester resin

As each of the polyolefin resins described above, polyolefin resinsusing metallocene catalysts were used for any of the cases. TABLE 1Resin composition Resin No. Resin Composition PES1 Polyethyleneterephthalate (IV value: 0.75) PES2 Polyethylene terephthalate (IVvalue: 0.82) PES3 Polyethylene terephthalate (IV value: 1.1) PES4Ethylene terephthalate - ethylene isophthalate copolymer (ethyleneisophthalate:: 5 mol %) (IV value: 0.9) PES5 Ethylene terephthalate -ethylene isophthalate copolymer (ethylene isophthalate:: 10 mol %) (IVvalue: 0.9) PES6 Ethylene terephthalate - ethylene isophthalatecopolymer (ethylene isophthalate:: 15 mol %) (IV value: 1.5) PES7Ethylene terephthalate - ethylene adiipate copolymer (ethylene adipate::10 mol %) (IV value: 0.6) PES8 Ethylene terephthalate - ethylenenaphthalate copolymer (ethylene-naphthalate: 10 mol %) (IV value: 0.9)PES9 Polybutylene terephthalate (IV value: 0.5) POL1 Polyethylene POL2Polypropylene POL3 Polybutene-1 POL4 Polyoctene-1 POL5Ethylene-propylene copolymer POL6 Ethylene-butene-1 copolymer POL7Ethylene-hexene copolymer POL8 Maleic acid anhydride copolymerizedpolyethylene POL9 Acrylic acid copolymerized polypropylene POL10Methylacrylate copolymerized polyethylene POL11 Diglycidyl methacrylatecopolymerized polyethylene PEL1 Ethylene-propylene polymerized elastomer(MFR: 0.4 g/10 min) PEL2 Ethylene-propylene polymerized elastomer (MFR:1 g/10 min) PEL3 Ethylene-propylene polymerized elastomer (MFR: 5 g/10min) PEL4 Ethylene-propylene polymerized elastomer (MFR: 10 g/10 min)PEL5 Ethylene-propylene polymerized elastomer (MFR: 30 g/10 min) PEL6Ethylene-propylene polymerized elastomer (MFR: 35 g/10 min)

TABLE 2 Thermoplastic resin-coated metal sheet Inner surface resin layerOuter surface Lower layer (blend resin) Melt Upper resin (TiO₂: POLGrain viscosity layer (PES) WT % content) Specimen Blend ratio Thicknesssize ratio Thickness Thickness No. Kind (%) (μm) (μm) V_(pol)/V_(pes)Type (μm) Type (μm) Metal sheet Section 1 PES1/POL8/PEL4 80/1/19 25 7 ×1.5 0.60 — — PES3 15 TFS Invention 2 PES1/POL8/PEL4 80/5/15 25 5 × 1.00.63 — — PES3 15 TFS Invention 3 PES2/POL9/PEL3 80/5/15 25 3 × 0.5 0.86— — PES3 15 TFS Invention 4 PES2/POL9/PEL2 85/5/10 28 8 × 1.0 1.10 — —PES3 15 TFS Invention 5 PES3/POL9/PEL1 80/10/10 30 6 × 0.8 0.71 — — PES315 TFS Invention 6 PES3/POL9/PEL1 75/10/15 20 14 × 3.1  1.25 — — PES3 15TFS Comp. Ex 7 PES4/POL10/POL1 80/7/13 35 10 × 2.0  0.80 — — PES3 15 ALInvention 8 PES3/POL11/POL2 80/15/5 25 4 × 0.8 0.61 — — PES3 15 ALInvention 9 PES6/POL8/POL3 80/5/15 20 6 × 0.9 0.19 — — PES3 15 ALInvention 10 PES7/POL8/POL1 80/10/10 25 5 × 0.6 0.88 — — PES3 15 ALInvention 11 PES9/POL9/PEL3 90/5/5 35 3 × 0.3 0.67 — — PES3 15 TFSInvention 12 PES9/POL10/PEL5 80/10/10 25 8 × 1.6 1.13 — — PES3 15 TFSInvention 13 PES2/POL9/POL4 80/10/10 25 5 × 0.8 0.72 — — PES3 15 TFSInvention 14 PES4/POL8/POL5 75/10/15 30 4 × 1.2 0.59 — — PES3 15 TFSInvention 15 PES2/POL1 99/1 30 8 × 1.8 0.62 — — PES3 15 TFS Invention 16PES3/POL1 95/5 20 7 × 1.5 0.23 — — PES3 15 TFS Invention

TABLE 3 Thermoplastic resin-coated metal sheet Inner surface resin layerOuter surface Lower layer (blend resin) Melt Upper resin (TiO₂: POLgrain viscosity layer (PES) WT % content Specimen Blend ratio Thicknesssize ratio Thickness Thickness Metal No. Kind (%) (μm) (μm) Vpol/VpesKind (μm) Kind (μm) sheet Section 17 PES2/POL2 85/15 30 7 × 1.6 0.65 — —PES3 15 TFS Invention 18 PES4/POL3 90/10 20 6 × 1.2 0.58 PES3 15 PES3 15ET Invention 19 PES5/POL1 90/10 20 5 × 1.5 0.62 PES3 15 PES3 15 ETInvention 20 PES2/POL9 85/15 25 4.5 × 0.2   0.30 — — PES3 15 ALInvention 21 PES3/POL8 80/20 25 4 × 0.3 0.32 — — PES3 15 AL Invention 22PES4/POL8 85/15 28 3.5 × 0.2   0.32 — — PES3 15 AL Invention 23PES5/PEL3 70/30 28 3 × 0.4 0.28 — — PES3 15 AL Invention 24 PES2/POL780/20 15 7 × 0.8 0.35 PES3 20 PES3 15 ET Invention 25 PES8/POL6 90/10 156 × 0.9 0.30 PES3 20 PES3 15 ET Invention 26 PES2/PEL4 90/10 20 6 × 0.80.26 — — PES3 15 TFS Invention 27 PES1 — 25 — — — — PES3 15 TFS Comp. Ex28 PES2/POL1 99.5/0.5  25 7 × 1.5 0.62 — — PES3 16 TFS Comp. Ex 29PES5/POL2 65/35 25 12 × 3.0  0.57 — — PES3 16 TFS Comp. Ex 30 PES4 — 25— — — — PES3 16 TFS Comp. Ex 31 PES2/PEL6 80/20 30 5 × 1.2 0.05 — — PES316 TFS Comp. Ex 32 PES1/PEL1 85/15 28 15 × 3.0  4.20 — — PES3 16 TFSComp. Ex

The thermoplastic resin-coated metal sheet obtained as described abovewas formed into a can of a bottomed cylindrical shape by using athickness-reducing drawing and ironing as described below.

After punching a thermoplastic resin-coated metal sheet into a blank of160 mm diameter, a drawn can with 100 mm can bottom diameter was formedsuch that the white polyester resin-coated surface was on the outersurface of the can. Then, it was re-drawn into a re-drawn can with 80 mmcan bottom diameter. Further, the re-drawn can was applied withstretching and, at the same time, ironing by composite fabrication toform a drawn and ironed can with 65 mm can bottom diameter. Thecomposite fabrication was conducted under the conditions that thedistance between the re-drawn portion and the upper end of the can was20 mm, the R portion at the shoulder of a re-drawing dice was 1.5 timesthe sheet thickness, a clearance between the re-drawing dice and a punchwas 1.0 times the sheet thickness and the clearance at the ironedportion was 50% of the original thickness. Then, an upper portion of thecan was trimmed by a known method and applied with neck-in fabricationand flange fabrication.

Then, methods of evaluating the thermoplastic resin and thethermoplastic resin-coated metal sheet are to be explained.

(Size of Polyolefin Resin Dispersed in Polyester Resin)

A Blend resin layer of the thermoplastic resin-coated metal sheet wasobserved under a scanning type electron microscope to measure the sizeof the fibrous resin. The measured value shows an average value measuredat three time points, that is, during coating or during filmpreparation, completion of coating or five min before completion of filmpreparation, at three positions, that is, 5 cm from both ends and at thecentral portion in view of the lateral direction of the resin-coatedmetal sheet. In Tables 2 and 3, it is represented by “length in theresin extruding direction” (μm)×“length in the direction perpendicularto resin extruding direction” (μm).

(Appearance for the can Inner Surface)

The can inner surface formed by the thickness-reducing drawing andironing fabrication method was observed with naked eyes, and presence orabsence of fibrous unevenness of the polyolefin resin in the resin layerand the transparency of the resin layer were evaluated by the followingstandards.

-   ◯: no fibrous unevenness was observed and it had sufficient    -   transparency-   Δ: fibrous unevenness was observed slightly, or slight clouding of    the resin layer was observed-   X: fibrous unevenness is observed, clouding of the resin layer was    observed.    (Melt Flow Rate of Polyolefin Elastomer)

Melt flow rate (230° C.) was measured by a customary method.

(Thickness of Resin Film)

The thermoplastic resin-coated metal sheet was buried in an epoxy typeembedding resin, sliced to a thickness of 5 μm and the cross section wasmeasured by microscopic observation.

(Intrinsic Viscosity (IV Value))

After dissolving the polyester resin in a 1:1 mixed solution ofphenol/tetrachloroethane, the specific viscosity was measured in athermostable bath at 30° C. by a Ubbelohde's viscometer to determine anintrinsic viscosity.

(Melt Viscosity)

The melt viscosity was determined by a capillary rheometer according toJIS K 7199.

(Fabricability)

Can formed by using a thickness-reducing drawing and ironing method wasobserved with naked eyes and the fabricability was evaluated based onthe following standards.

-   ⊚: fine crack or film breakage was not recognized-   ◯: slight fine crack to an extent not causing practical problems was    recognized-   Δ: crack and film breakage to an extent causing practical problem    was recognized-   X: broken upon forming    (Impact Resistance at Low Temperature)

After forming by using the thickness-reducing drawing and ironingmethod, trimming an upper portion of a can, and applying necking-in andflange fabrication, acidic drinks (Acerola drink, trade name ofproducts: manufactured by Nichirei Co.) at pH 2.6 were filled, aged at37° C. for one month and then seal was opened. The can was cut out fromthe upper end thereof in a circumferential direction at a width of 30 mmto form a specimen. After immersing the specimen in iced water for 5min, it was taken out and a steel rod attached with steel balls each of{fraction (1/2)} inch diameter at the top end at 15 mm distance in thecircumferential direction (weight: 1 kg) was dropped from the height of40 mm, a sponge impregnated with an aqueous 3% sodium chloride solutionwas abutted against generated convex portions on the can inner surface,a DC current at 6.3 V was applied to the specimen, the value of theflowing current was measured and the impact resistance at lowtemperature was measured by the following standards depending on themagnitude of the measured current value.

-   ⊚: less than 0.05 mA-   ◯: 0.05 mA or more and less than 0.1 mA-   Δ: 0.1 mA or more and less than 0.3 mA-   X: 0.3 mA or more    (Corrosion Resistance)

After forming by using a thickness-reducing drawing and ironing method,an upper portion of a can was trimmed and applied with neck-in andflange fabrication. Then after filling acidic drinks (Acelora drink,trade name of products: manufactured by Nichirei Co.), impact wasapplied at a low temperature from the outside of the can to the wall ofthe can in the same manner as practiced in the evaluation of the impactresistance at low temperature to form a concave portion. Then, afteraging at 37° C. for one month, seal was opened and concentration ofleached metal was measured by atomic absorption spectroscopy and thecorrosion resistance was evaluated in accordance with the followingstandards depending on the concentration.

-   ⊚: less than 0.3 ppm,-   ◯: more than 0.3 ppm and less than 0.5 ppm,-   Δ: more than 0.5 ppm and less than 1.0 ppm,-   X: 1.0 ppm or more

The result of evaluation was shown in Tables 4 and 5.

As shown in Table 4 and Table 5, it can be seen that any of thethermoplastic resin-coated metal sheets of the present invention isexcellent in the fabricability and shows favorable impact resistance atlow temperature and corrosion resistance. TABLE 4 Result ofcharacteristic evaluation Result of characteristic evaluation ImpactSpec- resistance imen at low Corrosion Resin No. Fabricabilitytemperature resistance unevenness Section 1 ⊚ ⊚ ⊚ ◯ Invention 2 ⊚ ⊚ ⊚ ◯Invention 3 ⊚ ⊚ ⊚ ◯ Invention 4 ⊚ ◯ ◯ ◯ Invention 5 ⊚ ◯ ⊚ ◯ Invention 6⊚ X ◯ X Comp. Ex 7 ⊚ ⊚ ⊚ ◯ Invention 8 ⊚ ◯ ⊚ ◯ Invention 9 ⊚ ⊚ ⊚ ◯Invention 10 ⊚ ⊚ ⊚ ◯ Invention 11 ⊚ ⊚ ⊚ □ Invention 12 ⊚ ◯ ◯ ◯ Invention13 ⊚ ⊚ ⊚ ◯ Invention 14 ⊚ ⊚ ⊚ ◯ Invention 15 ⊚ ◯ ◯ ◯ Invention 16 ⊚ ⊚ ◯◯ Invention

TABLE 5 Result of characteristic evaluation Result of characteristicevaluation Impact Spec- resistance imen at low Corrosion Resin No.Fabricability temperature resistance unevenness Section 17 ⊚ ⊚ ◯ ◯Invention 18 ⊚ ⊚ ⊚ ◯ Invention 19 ⊚ ⊚ ⊚ ◯ Invention 20 ⊚ ⊚ ⊚ ◯ Invention21 ⊚ ⊚ ⊚ ◯ Invention 22 ⊚ ⊚ ⊚ ◯ Invention 23 ◯ ◯ ◯ ◯ Invention 24 ⊚ ⊚ ⊚◯ Invention 25 ⊚ ⊚ ⊚ ◯ Invention 26 ⊚ ⊚ ⊚ ◯ Invention 27 ⊚ X Δ ◯ Comp.Ex 28 ⊚ X Δ ◯ Comp. Ex 29 ◯ Δ ◯ Δ Comp. Ex 30 ⊚ X Δ ◯ Comp. Ex 31 ⊚ X Δ◯ Comp. Ex 32 ◯ X Δ Δ Comp. Ex

Example 2

(Specimen Nos. 33-38, 43-53)

A long strip-like electrolytic chromic acid treated steel sheet (TFS)was re-wound from an uncoiler at a rate of 150 m/min and heated, andpellets of the polyester resin (PES), the polyolefin resin (POL) and/orpolyolefin elastomer (PEL) or only of the polyester resin shown in Table6 were heat melted at a temperature higher by about 30° C. than themelting point of the polyester resin while varying the kneading time byusing an extruder to form a blend resin, fed to a T-die and extruded onone surface of TFS to be an inner surface of a can (inner surface).Simultaneously, pellets of the polyester resin incorporated with 20% byweight of white titanium dioxide shown in Tables 7 and 8 were heatmelted at a temperature higher by about 30° C. than the melting point ofthe polyester resin by using an extruder, then fed into a T-die andextruded on the other surface of the heated TFS to be an outer surfaceof the can (outer surface) from the die nozzle. Then, a pair of pressbonding rolls were used and after sandwiching TFS having resin layersextruded on both surfaces thereof, it was quenched directly in water toprepare thermoplastic resin-coated metal sheets of Specimens Nos. 33-38,43-53 in Table 7 and Table 8.

(Specimen Nos. 39-42)

A long strip-like tin sheet (ET) was re-wound from an uncoiler at a rateof 150 m/min and heated, and pellets of the polyester resin and thepolyolefin resin shown in Table 6 were heat melted at a temperaturehigher by about 30° C. than the melting point of the polyester resinwhile varying the kneading time by using extruder to form a blend resin,the polyester resin shown in Table 6 was heat melted at a temperaturehigher by about 30° C. than the melting point of the polyester resin byusing a separate extruder, fed to a T-die having two die nozzles, andcoextruded on one surface of a tin sheet to be an inner surface of a canfrom the die nozzles such that the blend resin layer containing thepolyolefin resin was in contact with the tin sheet. Simultaneously,pellets of the polyester resin incorporated with 20% by weight of whitetitanium dioxide shown in Table 7 were heat melted at a temperaturehigher by about 30° C. than the melting point of the polyester resin byusing an extruder, fed into a T-die and extruded on the other surface ofthe heated tin sheet to be an outer surface of the can from a dienozzle. Then, a pair of press bonding rolls were used and aftersandwiching the tin sheet having resin layers extruded on both surfaces,it was quenched directly in water to prepare thermoplastic resin-coatedmetal sheets of Specimen Nos. 39-42 in Table 7.

(Specimen Nos. 54-58)

Pellets of the polyester resin and the polyolefin resin or thepolyolefin elastomer shown in Table 6 were heat melted at a temperaturehigher by about 30° C. than the melting point of the polyester resinwhile varying kneading time by using an extruder to form a blend resin,then fed to a T-die, extruded from a die nozzle, followed by trimmingand taken up as a non-orientation film to a coiler. Further, pellets ofthe polyester resin incorporated with 20% by weight of white titaniumdioxide shown in Table 8 were heat melted at a temperature higher byabout 30° C. than the melting point of the polyester resin by using anextruder, fed into a T-die, extruded from a die nozzle, followed bytrimming and was taken up as a non-orientation film to an uncoiler.Then, a long strip-like aluminum alloy sheet (AL) was re-wound at a rateof 150 m/min from the uncoiler and the blend resin film was abuttedwhile rewinding from the coiler to one surface thereof to be the innersurface of a can and, simultaneously, white polyester film was abuttedwhile being re-wound from the coiler against the other surface to be theouter surface of the can. Then, a pair of press bonding rolls were usedand after sandwiching the aluminum alloy sheet having resin layersextruded on both surfaces, it was quenched directly in water to preparethermoplastic resin-coated metal sheets of Specimen Nos. 54-58 in Table8.

(Specimen Nos. 59-61)

Pellets of the polyester resin and the polyolefin resin and/or thepolyolefin elastomer shown in Table 9 were heat melted at a temperaturehigher by about 30° C. than the melting point of the polyester resinwhile varying the kneading time by using an extruder to form a blendresin, pellets of the polyester (PES4) in Table 6 were heat melted to atemperature higher by about 30° C. than the melting point of therespective polyester resins by using separate extruders respectively,then fed to a die having two nozzles, co-extruded from the die nozzlessuch that the upper layer comprised of PES4 and the lower layercomprised of the blend resin, followed by trimming and then taken up toa coiler as a two-layered non-orientation film. Further, pellets of thepolyester resin incorporated with 20% by weight of white titaniumdioxide shown in Table 9 were heat melted at a temperature higher byabout 30° C. than the melting point of the polyester resin by using anextruder, fed to a T-die, extruded from a die nozzle, followed bytrimming and taken up as a non-orientation film to a coiler. Then, along strip-like TFS was re-wound from an uncoiler at a rate of 150 m/minand heated, and the two-layered resin film was abutted while beingre-wound from the coiler to one surface to be an inner surface of a canand, at the same time, the white polyester film was abutted while beingre-wound from the coiler against the other surface to be an outersurface of the can. Then, after sandwiching the TFS having resin layersextruded on both surfaces by using a pair of press bonding rolls, it wasquenched directly in water to prepare thermoplastic resin-coated metalsheets of Specimen Nos. 59-61 in Table 9.

(Specimen Nos. 62-64)

Pellets of the polyester resin and the polyolefin resin and/or thepolyolefin elastomer shown in Table 10 were heat melted at a temperaturehigher by about 30° C. than the melting point of the polyester resinwhile varying the kneading time by using an extruder to form a blendresin, pellets of the polyester PES4 and PES6 in Table 6 were heatmelted to a temperature higher by about 30° C. than the melting point ofthe respective polyester resins by using separated extrudersrespectively, then fed to a die having three nozzles, co-extruded fromthe die nozzles such that the upper layer comprised of PES4, theintermediate layer comprised of the blend resin, and the lower layercomprised of the PES6, followed by trimming and then taken up to acoiler as a three-layered non-orientation film. Further, pellets of thepolyester resin incorporated with 20% by weight of white titaniumdioxide shown in Table 9 were heat melted at a temperature higher byabout 30° C. than the melting point of the polyester resin by using anextruder, fed to a T-die, extruded from die nozzle, followed by trimmingand taken up as a non-orientation film to a coiler. Then, a longstrip-like TFS was re-wound from an uncoiler at a rate of 150 m/min andheated, and the three-layered resin film was abutted while beingre-wound from the coiler to one surface to be an inner surface of a canand, at the same time, the white polyester film was abutted while beingre-wound from the coiler against the other surface to be an outersurface of the can. Then, after sandwiching the TFS having resin layersextruded on both surfaces by using a pair of press bonding rolls, it wasquenched directly in water to prepare thermoplastic resin-coated metalsheets of Specimen Nos. 62-64 in Table 10.

In Tables 7-10, the outer surface resin layer contains 20% by weight ofTiO₂ as a white pigment. TABLE 6 Resin composition Resin No. ResinComposition PES1 Polyethylene terephthalate (IV value: 0.75) PES2Polyethylene terephthalate (IV value: 0.82) PES3 Polyethyleneterephthalate (IV value: 1.1) PES4 Ethylene terephthalate/ethyleneisophthalate copolymer (ethylene-isophthalate:: 5 mol %) (IV value: 0.9)PES5 Ethylene terephthalate/ethylene isophthalate copolymer (ethyleneisophthalate:: 10 mol %) (IV value: 0.9) PES6 Ethyleneterephthalate/ethylene isophthalate copolymer (ethylene isophthalate::15 mol %) (IV value: 1.5) PES7 Ethylene terephthalate/ethylene adipatecopolymer (ethylene adipate:: 10 mol %) (IV value: 0.5) PES8 Ethyleneterephthalate - ethylene naphthalate copolymer (ethylene-naphthalate: 10mol %) (IV value: 0.9) PES9 Polybutylene terephthalate (IV value: 1.35)POL1 Polyethylene POL2 Polypropylene POL3 Polybutene-1 POL4 Polyoctene-1POL5 Ethylene-propylene copolymer POL6 Ethylene-butene-1 copolymer POL7Ethylene-hexene copolymer PEL1 Ethylene/propylene polymerized elastomer(MFR: 0.45 g/10 min) PEL2 Ethylene/propylene polymerized elastomer (MFR:0.8 g/10 min) PEL3 Ethylene/propylene polymerized elastomer (MFR: 6 g/10min) PEL4 Ethylene/propylene polymerized elastomer (MFR: 12 g/10 min)PEL5 Ethylene/propylene polymerized elastomer (MFR: 25 g/10 min) PEL6Ethylene/propylene polymerized elastomer (MFR: 30 g/10 min)

TABLE 7 Thermoplastic resin-coated metal sheet Outer surface Innersurface resin layer resin layer Specimen Blend ratio Thickness ThicknessMetal No. Type (wt %) (μm) Type (μm) sheet Section 33 PES4/PES9/POL530/50/20 25 PES4 15 TFS Invention 34 PES5/PES9/POL5 50/47/3 25 PES4 15TFS Comp. Ex 35 PES5/PES9/POL5 50/45/5 25 PES4 15 TFS Invention 36PES5/PES9/POL5 30/50/20 25 PES4 15 TFS Invention 37 PES5/PES9/POL525/50/30 25 PES4 15 TFS Invention 38 PES5/PES9/POL5 20/45/35 25 PES4 15TFS Comp. Ex 39 PES6/PES9/POL5 30/50/20 25 PES4 15 ET Invention 40PES6/PES9/POL1/POL5 30/50/10/10 25 PES4 15 ET Invention 41PES6/PES9/PEL3 30/50/20 25 PES4 15 ET Invention 42 PES6/PES9/POL5/PEL330/50/10/10 25 PES4 15 ET Invention 43 PES4/POL5 80/20 25 PES4 15 TFSInvention 44 PES5/PES9/POL2 30/50/20 25 PES4 15 TFS Invention 45PES5/PES9/POL3 50/30/20 25 PES4 15 TFS Invention 46 PES5/PES9/POL430/50/20 25 PES4 15 TFS Invention

TABLE 8 Thermoplastic resin-coated metal sheet Outer surface Innersurface resin layer resin layer Specimen Blend ratio Thickness ThicknessMetal No Type (wt %) (μm) Type (μm) sheet Section 47 PES5/PES9/POL630/50/20 25 PES4 15 TFS Invention 48 PES5/PES9/POL7 30/50/20 25 PES4 15TFS Invention 49 PES5/PES9/PEL1 30/50/20 25 PES4 15 TFS Comp. ex 50PES5/PES9/PEL2 30/50/20 25 PES4 15 TFS Invention 51 PES5/PES9/PEL430/50/20 25 PES4 15 TFS Invention 52 PES5/PES9/PEL5 30/50/20 25 PES4 15TFS Invention 53 PES5/PES9/PEL6 30/50/20 25 PES4 15 TFS Comp. ex 54PES1/PES9/PEL5 30/50/20 25 PES4 15 AL Invention 55 PES2/PES9/POL1/PEL430/50/10/10 25 PES4 15 AL Invention 56 PES3/PES9/POL5/PEL4 30/50/5/15 25PES4 15 AL Invention 57 PES7/PES9/POL5/PEL5 30/50/10/10 25 PES4 15 ALInvention 58 PES8/PES9/POL6/PEL3 30/50/10/10 25 PES4 15 AL Invention

TABLE 9 Thermoplastic resin-coated metal sheet Inner surface resin layerUpper layer Lower layer Outer surface Specimen Thickness Blend ratioThickness resin layer No. Type (μm) Type (wt %) (μm) Type ThicknessMetal sheet Section 59 PES 5 PES6/PES9/POL5 30/50/20 25 PES4 15 TFSInvention 60 PES 5 PES6/PES9/POL1/PEL3 30/50/10/10 25 PES4 15 TFSInvention 61 PES 5 PES6/PES9/PEL2 30/50/20 25 PES4 15 TFS Invention

TABLE 10 Thermoplastic resin-coated metal sheet Inner surface resinlayer Outer surface Upper layer Intermediate layer Lower layer resinlayer Specimen Thickness Blend ratio Thickness Thickness Thickness No.Type (μm) Type (wt %) (μm) Type (μM) Type (μm) Metal sheet Section 62PES4 5 PES6/PES9/PEL4 30/50/20 20 PES6 5 PES4 15 TFS Inveniton 63 PES4 5PES6/PES9/POL1/PEL2 30/50/10/10 20 PES6 5 PES4 15 TFS Inveniton 64 PES45 PES6/PES9/PEL3 30/50/20 20 PES6 5 PES4 15 TFS Inveniton

TABLE 11 Result of characteristic evaluation Result of characteristicevaluation Specimen Low temperature Corrosion No. Fabricability impactresistance resistance Section 33 ⊚ ⊚ ⊚ Invention 34 ◯ X Δ Comp. Ex 35 ⊚⊚ ⊚ Invention 36 ⊚ ⊚ ⊚ Invention 37 ⊚ ⊚ ⊚ Invention 38 ⊚ X Δ Comp. Ex 39⊚ ⊚ ⊚ Invention 40 ⊚ ⊚ ⊚ Invention 41 ⊚ ⊚ ⊚ Invention 42 ⊚ ⊚ ⊚ Invention43 ⊚ ◯ ◯ Invention 44 ⊚ ⊚ ⊚ Invention 45 ⊚ ⊚ ⊚ Invention 46 ⊚ ⊚ ⊚Invention 47 ⊚ ⊚ ⊚ Invention 48 ⊚ ⊚ ⊚ Invention

TABLE 12 Result of characteristic evaluation Result of characteristicevaluation Specimen Low temperature Corrosion No. Fabricability impactresistance resistance Section 49 Δ X ◯ Comp. Ex 50 ⊚ ⊚ ⊚ Invention 51 ⊚⊚ ⊚ Invention 52 ⊚ ◯ ◯ Invention 53 ⊚ X Δ Comp. Ex 54 ⊚ ⊚ ⊚ Invention 55⊚ ⊚ ⊚ Invention 56 ⊚ ⊚ ⊚ Invention 57 ⊚ ⊚ ⊚ Invention 58 ⊚ ⊚ ⊚ Invention59 ⊚ ⊚ ⊚ Invention 60 ⊚ ⊚ ⊚ Invention 61 ⊚ ⊚ ⊚ Invention 62 ⊚ ⊚ ⊚Invention 63 ⊚ ⊚ ⊚ Invention 64 ⊚ ⊚ ⊚ Invention

Further, the three types of the metal sheets described above wereidentical with those used in Experiment Example 1 and any of thepolyolefin resins used was synthesized by means of metallocene catalyst.

Cans each of a bottomed cylindrical shape were formed using thethermoplastic resin-coated metal sheets obtained above in the samemanner as in Experiment Example 1 and thermoplastic resin coating andthe thermoplastic resin-coated metal sheet were evaluated in the samemanner as in Experimental Example 1 and the results are shown in Table11 and Table 12.

As shown in Table 11 and Table 12, it can be seen that any of thethermoplastic resin-coated metal sheets according to the presentinvention is excellent in the fabricability and shows favorable impactresistance at low temperature and corrosion resistance.

INDUSTRIAL APPLICABILITY

The present invention provides a thermoplastic resin-coated metal sheetin which a coating layer of a thermoplastic resin composition comprisinga blend a polyester resin and at least one of polyolefin ingredientsselected from the group consisting of polyolefin resins and polyolefinelastomers is formed on at least one surface of a metal sheet, and a canformed obtained by forming the same, the thermoplastic resin-coatedmetal sheet described above is excellent in the workability, and showsexcellent workability causing no crackings and peeling to the resinlayer even after being applied with severe forming such asthickness-reducing drawing or thickness-reducing drawing and ironing.Further, it shows excellent impact resistance at low temperature with nooccurrence of cracks in the resin layer even when applied with impact atlow temperature and, further, leaches less metals when the formed can isleft for a long time while being filled with acidic contents and showsexcellent corrosion resistance.

1. A thermoplastic resin-coated metal sheet in which a thermoplasticresin composition comprising a blend of polybutylene terephthalate and apolyolefin ingredient comprising at least one member selected from thegroup consisting of polyolefin resins and polyolefin elastomers iscoated in a substantially non-orientation state on at least one surfaceof a metal sheet.
 2. A thermoplastic resin-coated metal sheet accordingto claim 1, wherein a polyolefin resin is used as the polyolefiningredient.
 3. A thermoplastic resin-coated metal sheet according toclaim 1, wherein a polyolefin elastomer is used as the polyolefiningredient.
 4. A thermoplastic resin-coated metal sheet according toclaim 1, wherein a polyolefin resin and a polyolefin elastomer are usedas the polyolefin ingredient.
 5. A thermoplastic resin-coated metalsheet according to any one of claim 1, wherein the ratio of a melt indexof the polyolefin ingredient upon heat melting (VPOL) to that of thepolybutylene terephthalate upon heat melting (VPES), that is, VPOL/VPESis 1.2 or less in the thermoplastic resin composition.
 6. Athermoplastic resin-coated metal sheet according to claim 1, wherein apolybutylene terephthalate layer formed by coating the polybutyleneterephthalate in a substantially non-orientation state is formed on thecoating layer of the thermoplastic resin composition.
 7. A thermoplasticresin-coated metal sheet according to claim 1, wherein a polybutyleneterephthalate layer coating in which the polybutylene terephthalate isin a substantially non oriented state is formed on the surface of themetal sheet, and a coating layer of the thermoplastic resin compositionis formed on the polyester resin layer.
 8. A thermoplastic resin-coatedmetal sheet according to claim 1 wherein the polyolefin resin is a resincomprising one or more of 1-alkene polymer resins having a number orcarbon atoms of 2 to
 8. 9. A thermoplastic resin-coated metal sheetaccording to claim 8, wherein the 1-alkene polymer resin is one ofpolyethylene, polypropylene, and an ethylene-propylene copolymer.
 10. Athermoplastic resin-coated metal sheet according to claim 8, wherein thepolyolefin resin is a polyolefin resin polymerized by means of ametallocene catalyst.
 11. A thermoplastic resin-coated metal sheetaccording to claim 1, wherein at least a portion of the polyolefin resinis a modified polyolefin resin modified with one of maleic acidanhydride, acrylic acid, acrylic acid ester and diglycidyl methacrylate.12. A thermoplastic resin-coated metal sheet according to claim 1wherein the polyolefin elastomer is an in-plant producedethylene-propylene copolymerized elastomer having a melt flow rate (MFR,230° C.) of 0.4 to 30 g/10 min). 13-15. (canceled)
 16. A thermoplasticresin-coated metal sheet according to claims 1 to 12, wherein thethermoplastic resin composition contains 1 to 30% by weight of apolyolefin ingredient.
 17. A thermoplastic resin-coated metal sheetaccording to claim 1, wherein the thermoplastic resin compositioncontains 70 to 95% by weight of the polybutylene terephthalate.
 18. Athermoplastic resin-coated metal sheet according to claim 1, wherein thethermoplastic resin composition is heat melted and directly extrudedfrom a T-die to a metal sheet for coating.
 19. A thermoplasticresin-coated metal sheet according to claim 1, wherein the thermoplasticresin composition is heat melted, extruded from a T-die onto a castingroll, cooled to solidify into a film and then the film is hot pressbonded on a metal sheet.
 20. A thermoplastic resin-coated metal sheetaccording to claim 18, wherein, wherein the polyolefin ingredient in thecoating layer comprising a thermoplastic resin composition is presentbeing dispersed with a size of 1 to 10 μm in the extruding direction and0.1 to 2 μm in the direction perpendicular to the extruding direction.21. A thermoplastic resin-coated metal sheet according to claim 1,wherein the metal sheet is one of electrolytic chromic acid treatedsteel sheet, tin-plated sheet and aluminum alloy sheet.
 22. A can usinga thermoplastic resin-coated metal sheet according to claim 1.